Data from Tau Ceti is very tentative, but hints at a planet.

Most of the exoplanets we've discovered thus far have been found because they're easy to spot—Jupiter-sized giants orbiting close in to their host stars. But the Kepler mission has been providing a huge catalog of exoplanets and with it we've obtained a very different perspective, finding that planets in general are common and most of them are far smaller than the gas giants first identified. This new perspective has raised the prospect that we can identify some orbiting nearby stars, following identification with direct observations searching for signs that the planet's atmosphere is shaped by life.

More recently, astronomers have started making progress towards identifying planetary candidates that are close enough that we could eventually image them with an orbiting telescope. Just in October, astronomers announced there was a hint of a signal from an exoplanet in the light from one of the closest stars, Centauri B. Today the astronomers have released a paper that suggests there are several planets around the nearby star Tau Ceti, and one of them is likely to be within the star's habitable zone.

It's important to note the signals of the planets are buried deep in a variety of optical noise, both from the telescopes and instruments, and from the star itself. Further observations are going to be needed to confirm that the signals appear consistently. But this work certainly suggests those follow-up observations are going to be a high priority.

The Tau Ceti observations are based on what are called radial velocity measurements. As planets swing around a star during their orbits, they tug the star back and forth, accelerating it ever so slightly in various directions. If the planets' orbits are aligned so that the motion of the star occurs in the same plane as the Earth, this will cause a slight Doppler shift in the light that we receive from that star. The star's light will periodically appear somewhat bluer as it gets pulled towards Earth and redder when it's shifted away.

But these periodic changes can be very small. This is especially true when the plane of their orbits isn't close to edge-on from the perspective of Earth (which causes less of the star's motion to be in the same plane as Earth). But it will also be small when the planets are the sort of moderately sized, rocky bodies we'd be most interested in.

Adding to the challenge of detecting them, small motions in the instruments themselves can create a noise that obscures the signal. So can things like the rotation of the star (which brings brighter and darker regions to the fore) and long-term cycles in the star's activity. It takes a lot of effort to account for this noise (or, technically, "jitter") and find weak signals buried within it. So, the authors say they started out focusing on Tau Ceti simply because it's a very quiet, regular star. People had looked at it before and saw no hints of exoplanets, so it could provide a good test case for figuring out how to account for jitter.

In the past, one thing that researchers did was "bin" data, aggregating observations taken across several hours in order to average out short-term changes in the light we're seeing. The authors of the new paper suggested that this method, while getting rid of noise, could also be getting rid of some of the signal. So, they started with unbinned data and began trying to create a statistical model of the noise. Their procedure for doing this was to add signals for a number of planets to actual data from Tau Ceti. They then created various mathematical models of the noise and subtracted them from the data, trying to determine which models worked best (which turned out to be a combination of moving average and random white noise).

Once they had that in hand, the astronomers turned to the actual data from Tau Ceti without any added signals. And, this time, three signals did pop out, with each of them adding between 1010 and 1017 to the statistical fit with the real data. The authors concluded that there were three planets in this signal, orbiting with periods of 14, 35, and 94 days.

That's the most convincing part of their paper, but it wasn't the end of the paper. All of their initial data was obtained using the planet-finding HARPs instrument. But data on Tau Ceti had also been obtained using Hawaii's Keck telescope and the Anglo-Australian telescope in (you guessed it) Australia. These instruments had about three times the noise that the HARPS data did. When the authors checked the data from these instruments, they found... nothing, not even the planets they'd found in the earlier analysis.

Nevertheless, they went on and combined the data from all three instruments. A basic analysis didn't identify any signals, but they went ahead and started doing modeling, assuming their data contained noise and one or more planetary signals. The two planets at 13.9 and 94 days came out of the analysis with high significance, and the third also increased the fit of their model. But they kept going and found that adding two more planets to their model increased the fit, although not by nearly the same degree. One orbited with a period of 630 days, the second at 168 days. The latter one is the object that resides in Tau Ceti's habitable zone; it has a mass that's at least four times that of Earth's.

Even the authors admit that discussions about the planet, "remain merely speculative until the planetary origin of the signals can be verified by an independent detection." But there are a number of reasons to think that something is there. Tau Ceti has a bright debris disk that extends out to 55 Astronomical Units (55 times the average distance from the Earth to the Sun). These sorts of disks are thought to be the raw materials for planet formation. Tau Ceti is also a low-metal star (it doesn't have much beyond hydrogen and helium), which is in keeping with the fact that the signals suggest low-mass planets. And, finally, the specific configuration of planets detected in this study would be able to maintain stable orbits indefinitely.

Still, with planets this close to the limits of detecting, it's difficult not to remain a bit cautious for now (just as the authors have). Hopefully, a few more years of observations will help us know how much of this evidence is signal, and how much is noise.

I wonder if NASA really really tried, using all the tricks like gravity slingshots, disposable multi-stage rockets, refueling from ISS, etc, how fast they can get a satellite to another planet (in this case either Centauri or Ceti).

12 light years away? If there is any intelligent life that has advanced to an information age, I wonder if they have found out whether Gore or Bush won the recount yet?

I wonder how well that region, so close by, has been surveyed by SETI and other radio telescopes? If we haven't heard from that area, either that habitable zone planet isn't very habitable, there is no intelligent life yet, or they haven't advanced to that point yet. From the description of the metallicity, I presume Tau Ceti is a Population II star. Does current thinking suggest that the planets around such stars would not be capable of supporting life?

What is the point of the "artist's impression"? Basically, it's someone guessing what a planet they've never seen might look like, in a favourable light. Does the planet have oceans? No idea. Does it have plant life, and greenery? Who knows. Does its surface primarily consist of rusted iron? Possibly.

The artist's impression in situations like this, and when drawing pictures of "supernova 1997A", bears no relationship to reality and is just NASA or whomever having a bit of artistic licence.

I wonder if NASA really really tried, using all the tricks like gravity slingshots, disposable multi-stage rockets, refueling from ISS, etc, how fast they can get a satellite to another planet (in this case either Centauri or Ceti).

With current technology? Transit times of centuries. Look at the Voyager probes for instance; launched using huge boosters and using a whole series of gravitational slingshots, and they're only just now reaching the boundaries of our solar system, never mind racking up light years on the odometer.

I wonder if NASA really really tried, using all the tricks like gravity slingshots, disposable multi-stage rockets, refueling from ISS, etc, how fast they can get a satellite to another planet (in this case either Centauri or Ceti).

Tens of thousands of years using conventional rockets.

Maybe faster with a decent ion engine.

Essentially so slow as to be pointless right now. Might as well wait and see if we can develop faster propulsion system that would get a probe there in a fraction of the time.

I wonder if NASA really really tried, using all the tricks like gravity slingshots, disposable multi-stage rockets, refueling from ISS, etc, how fast they can get a satellite to another planet (in this case either Centauri or Ceti).

With current technology? Transit times of centuries. Look at the Voyager probes for instance; launched using huge boosters and using a whole series of gravitational slingshots, and they're only just now reaching the boundaries of our solar system, never mind racking up light years on the odometer.

While it's true that a craft like the Voyager probe would take centuries (actually about 52 millenia at the current rate) to reach such a far off planet, that isn't taking into account the leaps in technology and the fact that the Voyager probe was not designed for interstellar travel. With technologies like ion engines and solar/beam sails it is possible to propel a craft from our solar system at a sufficient velocity to reach a planet around tau ceti within a few generations (a small amount of time considering the distance).

What is the point of the "artist's impression"? Basically, it's someone guessing what a planet they've never seen might look like, in a favourable light. Does the planet have oceans? No idea. Does it have plant life, and greenery? Who knows. Does its surface primarily consist of rusted iron? Possibly.

The artist's impression in situations like this, and when drawing pictures of "supernova 1997A", bears no relationship to reality and is just NASA or whomever having a bit of artistic licence.

Edit: Oh, and we don't even know that said planet actually exists!

The rendered images always look like something out of a video game while ACTUAL images of planets and moons are plain or bland and set against the blackness of space. I think the general public would be better served having more realistic, ya know, sciency images.

Even uranium releases 500 000 MJ/kg (ie 500,000,000,000 per Kg), requiring 70,000 Kg of uranium to do this (with 100% efficiency). Now in fairness, total world supply of Uranium is about 5,000,000 tonnes, so if we diverted all the energy from uranium in the world to this we could do about 70 one way trips. Hopefully there is uranium at the other end to refuel for any return journey.

I'm not sure if my maths is 100% correct - but the energy involved is simply enormous to do this sort of trip, at least at 1g. Of course, you can do it at lower accelerations for less energy (eg., 0.01g gets you there in 67/69 years for just 1% of the energy), but not too many people are going to do such a trip...

In all seriousness, this is pretty cool, since it makes it easier to get more data about this planet, but don't fool yourself into thinking we are ever going to go there.

People at one point also thought we'd never be capable of powered flight but here we are. I know that somehow circumventing the light speed barrier is a bit harder, to put it mildly, but this is one of the few things I'm the eternal optimist regarding.

I wonder if NASA really really tried, using all the tricks like gravity slingshots, disposable multi-stage rockets, refueling from ISS, etc, how fast they can get a satellite to another planet (in this case either Centauri or Ceti).

Tens of thousands of years using conventional rockets.

Maybe faster with a decent ion engine.

Essentially so slow as to be pointless right now. Might as well wait and see if we can develop faster propulsion system that would get a probe there in a fraction of the time.

Arthur C. Clarke wrote a short story about a multigeneration spaceship that went to another planet with the intent to colonise it. When the Xth generation of humans aboard the spaceship finally arrived, they were welcomed by humans.

Turns out that a faster method of travel had been invented after their spaceship had left.

That system alone provides 22 % of the 9 acknowledged potential habitable planets! Tau Ceti joins Gliese 581 among the exclusive systems which have 2 habitables.

Reflecting on the thread above, for science purposes these planets, their eventual inhabitance and their constraints for life will all be studied from here. It will never be profitable to visit these systems.

But if we did, we wouldn't "screw it up". It is very unlikely exogenous life can get a foothold in an indigenous biosphere.

Already inhabited planets will likely never be visited, not cost effective for either science or colonization attempts. For the latter, you want psychroplanets like Mars that you can terraform, or better yet just use the much more accessible and less risky Oort cloud resources for habitats. This system in particular you don't want to visit, it has an observed debris disk that is an order of magnitude more dense than our own asteroid belt, so expect simple prokaryotes and not complex multicellulars. Planets: been there, done that.

The issue isn't technological because we've proven time and time again if it can be done we'll find a way. I think the real issue is political/sociological. I just dont think the will is there to attempt something like this, especially considering the low/unproven value in such a trip. What do we get out of it? Science for science sake rarely happens, at least at this magnitude. There'd have to be a real economic reason to go. Avatar, as goofy a movie as it is, is pretty accurate with the reason behind such a trip. If we find a reason worthy (such as minerals, etc.) you'll probably see a real push for going. Until then it's all wishful thinking.

edit This is assuming of course we will have exhausted all available resources closer to home. With all the resources in this solar system I can't see that happening for a long, long time. For it to happen anytime soon I'd think we would have to have undisputable proof of life. There just doesn't seem to be any realistic way otherwise.

In all seriousness, this is pretty cool, since it makes it easier to get more data about this planet, but don't fool yourself into thinking we are ever going to go there.

People at one point also thought we'd never be capable of powered flight but here we are. I know that somehow circumventing the light speed barrier is a bit harder, to put it mildly, but this is one of the few things I'm the eternal optimist regarding.

Warp Drive is achievable . NASA is already trying to figure out how to generate warp fields in small scale to someday power an actual warp drive. The math says it can be done. The technology just has to be solved. Once we have it, we can travel at speeds 10 times the speed of light. However, they will have to figure out how to deal with the buildup of particles the ship collects as they travel or they'll annihilate everything around its destination. We could travel to Tau Ceti in little as 1 year, 2 months, and 13 days. That's a short time for travelling 70 trillion miles.

Arthur C. Clarke wrote a short story about a multigeneration spaceship that went to another planet with the intent to colonise it. When the Xth generation of humans aboard the spaceship finally arrived, they were welcomed by humans.

Turns out that a faster method of travel had been invented after their spaceship had left.

Given the distances between stars, I can totally see that happening. Even if we were able to put humans into some sort of cryogenic sleep, imagine the advancement of the species in tens of thousands of years. Even humans were already there to greet them, they would probably seem quite alien to those who arrived on such a journey.

Warp Drive is achievable . NASA is already trying to figure out how to generate warp fields in small scale to someday power an actual warp drive. The math says it can be done.

No, we can never go ftl. As one theorist said on wormholes, roughly: sure, maybe you can solve the technology, but then our whole universe implodes. No kidding, time travel and even by ftl means, destabilizes the lightcone of causal spacetime.

But we also know from math that warp fields specifically doesn't work. These solutions has spacetime volumes traveling at ftl when they are born. How do you propose to get them above ftl in the first place? It is a bootstrap solution without the strap...

Why would we have to send people instead of a rover? Particularly for the first trip to another potentially habitable planet. For a rover, 60 years shouldn't be such a huge deal. Voyager is half that age already, and still providing useful information. If technology really gives us a much faster drive, we can always send a second probe after it... or maybe we'll have found even more habitable planets by then that would make good destinations.

What is the point of the "artist's impression"? Basically, it's someone guessing what a planet they've never seen might look like, in a favourable light. Does the planet have oceans? No idea. Does it have plant life, and greenery? Who knows. Does its surface primarily consist of rusted iron? Possibly.

The artist's impression in situations like this, and when drawing pictures of "supernova 1997A", bears no relationship to reality and is just NASA or whomever having a bit of artistic licence.

Edit: Oh, and we don't even know that said planet actually exists!

The rendered images always look like something out of a video game while ACTUAL images of planets and moons are plain or bland and set against the blackness of space. I think the general public would be better served having more realistic, ya know, sciency images.

I'm not so sure the public would be better served with "sciency" images. I think that if one has the requisite understanding of planetary science to appreciate the significance of planets in the habitable then "sciency" images are appropriate, but for the average layperson they have no relevance. It's hard to sell a multi-billion dollar trip to a collection of slight "jitters", but slap an alluring image on it and people will want to go. I'm not suggesting that we deliberately mislead the public into funding such a mission, just that people often want to see their goal, even if it's not an accurate representation. For example, the first Mars mission (Mariner 4) was launched with the thought that we might see oceans, flora, fauna, or even civilizations on Mars. Though no such thing happened, subsequent missions proved that Mars was still worth exploring, and public interest in Mars has only increased in recent years with the Spirit, Opportunity, and Curiosity rovers.

Why would we have to send people instead of a rover? Particularly for the first trip to another potentially habitable planet. For a rover, 60 years shouldn't be such a huge deal. Voyager is half that age already, and still providing useful information. If technology really gives us a much faster drive, we can always send a second probe after it... or maybe we'll have found even more habitable planets by then that would make good destinations.

For the current Mars rover tech, we send commands up and wait between 10 and 40 minutes before we see the rover start to move (because it takes between 5 and 20ish minutes for radio waves to cross the distance between Earth and Mars, depending on their relative positions in their orbits around the Sun). Applying the same mission profile to a Tau Ceti mission, we would send a command and our children would see the rover execute that command 24 years later*, assuming the rover's still working by the time the message arrives. Not really a practical way to operate a rover, unless we find some means of FTL communication. For this reason, any rover would need to be fully automated, and doing that means deciding what you want to study before you've even seen what's there.

* Edit: 12 Years for the command to cross 12 LY of space, and 12 years for the video and data to be transmitted back, assuming we can even build an antenna with sufficiently high gain and pointing precision and make it lightweight enough so it can still be packaged in a ship that needs to be accelerated to a significant fraction of the speed of light.

To quote Douglas Adams: "Space is big. You just won't believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space."

Why would we have to send people instead of a rover? Particularly for the first trip to another potentially habitable planet. For a rover, 60 years shouldn't be such a huge deal. Voyager is half that age already, and still providing useful information. If technology really gives us a much faster drive, we can always send a second probe after it... or maybe we'll have found even more habitable planets by then that would make good destinations.

If you thought "7 minutes of terror" was a horrible wait don't forget to add "12 years of terror" before you can conceivably receive signal from the probe.

A rover would be risky, considering you have no idea what the surface is like. The actual travel time would be longer, in order to decelerate for orbital insertion or attempt at landing. The easiest thing to do would be a flyby.

Still, if we launch it now, we might hear from it by the time Half Life 3 comes out.

So rather than wait for FTL spaceships, we just wait for Artificial Intelligence good enough to out-perform a human astronaut, and send that. It might take centuries to get there, and 12 years to report back, but the Human race would learn as much as by sending a manned mission at a fraction of the price (No food, water, air or living quarters required).

In all seriousness, this is pretty cool, since it makes it easier to get more data about this planet, but don't fool yourself into thinking we are ever going to go there.

People at one point also thought we'd never be capable of powered flight but here we are. I know that somehow circumventing the light speed barrier is a bit harder, to put it mildly, but this is one of the few things I'm the eternal optimist regarding.

People never thought we'd be able to go to the moon, and look at us now. Oh wait.

Warp Drive is achievable . NASA is already trying to figure out how to generate warp fields in small scale to someday power an actual warp drive. The math says it can be done.

No, we can never go ftl. As one theorist said on wormholes, roughly: sure, maybe you can solve the technology, but then our whole universe implodes. No kidding, time travel and even by ftl means, destabilizes the lightcone of causal spacetime.

But we also know from math that warp fields specifically doesn't work. These solutions has spacetime volumes traveling at ftl when they are born. How do you propose to get them above ftl in the first place? It is a bootstrap solution without the strap...

And before we broke the sound barrier, people thought that was impossible to. There is research on "FTL" at NASA based off of Alcubierre's theory. Below is a link to the NASA paper.

On a side note, I know Dr. White. We work in the same building at JSC. He's in the engineering directorate and I work in the Human Health and Performance Directorate.

So rather than wait for FTL spaceships, we just wait for Artificial Intelligence good enough to out-perform a human astronaut, and send that. It might take centuries to get there, and 12 years to report back, but the Human race would learn as much as by sending a manned mission at a fraction of the price (No food, water, air or living quarters required).

Aside from the large energy source needed to sustain the computer in which it lived, such an AI would also need facilities to perform maintenance on its own circuitry to repair damage caused by radiation exposure, among other necessities. Effectively, you would still be building living quarters and/or suspended animation facilities for a sentient being, albeit an artificial one. Robotic missions don't scale well to interstellar distances, full stop.

I'm not sure if my maths is 100% correct - but the energy involved is simply enormous to do this sort of trip, at least at 1g

You forgot the rocket equation. Most of the mass to start will be fuel, and it takes extra fuel to accelerate the fuel to accelerate the fuel to accelerate the fuel etc.

Actually, I didn't even try to imagine the propulsion system. I just assumed at you could get fission energy from uranium, so the mass decrease would only be 1/3 of a kg I think. But I agree you then have to propel the system, but that may be possible in other ways (such as by emitting light from one side of your spaceship only). Even if it is, and I'm not saying that's true, the energy required is staggering.